Mixing or blending of preformed PU with various preformed polymers (epoxies, polyacrylates, poly(acrylonitrile-butadiene), polystyrene, etc.) are known. See, e.g., U.S. Pat. No. 4,302,553, to Frisch et al. Chem. Abs. 103(4): 23157r discloses a blend of preformed PU/PVC. A physical blend of PU/PVC is also disclosed in Garcia, D., J. Polym. Sci., Part B: Polym. Phys., 24(7), 1577-86.
Thermoplastic PU's melt-blended with PVC in a Banbury mixer are reported by Gifford, K. R.; Moore, D. R.; and Pearson, R. G. (Chem. Abs. 94(12): 85402w.) See also Khachatryan, P. M. et al, Chem. Abs. 105(16): 134778e.
Physically blending a preformed PU with a pregelled PVC cannot possibly achieve the degree of interpenetration obtained in our method.
Pernice et al, supra, make an IPN by reacting (I) a mix of poly(oxypropylene) triol, ethylene oxide capped and grafted with acrylonitrile, and a mixture of short chain diols with (II) an isocyanate (a "modified MDI") in admixture with (III) a preformed epoxy. A PU network is said to be formed within the epoxy network.
We point out certain distinctions between our IPN and those of the prior art: We do not mix together a PU resin with a pregelled PVC as starting materials. That is to say, we do not take a preformed PU and blend it with a pregelled PVC, or vice versa. Nor do we have a solvent or emulsion system. Nor do we form both networks simultaneously. Nor do we have a PU film overlaid by a PVC film, or vice versa. Finally, our PVC must initially be in the form of a plastisol. "Plastisols are produced by dispersion of a fine particle size PVC resin in plasticizer." --Sarvetnick, Harold A., Polyvinyl Chloride, p. 173.